Biological Soil Disinfestation Research Articles

Clostridium omnivorum sp. nov., isolated from anoxic soil under the treatment of reductive soil disinfestation.

Reductive soil disinfestation (RSD), also known as biological soil disinfestation, is a bioremediation method used to suppress soil-borne plant pathogens by stimulating the activity of indigenous anaerobic bacteria in the soil. An anaerobic bacterial strain (E14T) was isolated from an anoxic soil sample subjected to RSD treatment and then comprehensively characterized. Cells of the strain were Gram-stain-positive, curved to sigmoid, and spore-forming rods. Cells were motile with a polar flagellum. Strain E14T grew in peptone-yeast extract broth, indicating that it utilized proteinous compounds. Strain E14T was also saccharolytic and produced acetate, isobutyrate, butyrate, isovalerate and gases (H2 and CO2) as fermentation products. The strain did not decompose any of examined polysaccharides except for starch. The major cellular fatty acids of strain E14T were iso-C15:0 and iso-C15:0 DMA. The closest relative to strain E14T, based on 16S rRNA gene sequences, was Clostridium thermarum SYSU GA15002T (96.2 %) in the Clostridiaceae. Whole-genome analysis of strain E14T showed that its genome was 4.66 Mb long with a genomic DNA G+C content of 32.5 mol%. The average nucleotide identity (ANIb) between strain E14T and C. thermarum SYSU GA15002T was 69.0 %. The presence of the genes encoding glycolysis and butyrate production via the acetyl-CoA pathway was confirmed through genome analysis. Based on the obtained phylogenetic, genomic and phenotypic data, we propose that strain E14T should be assigned to the genus Clostridium in the family Clostridiaceae as Clostridium omnivorum sp. nov. The type strain is E14T (=NBRC 115133T=DSM 114974T).

Correction: The impact of biological soil disinfestation in conjunction with antagonists and organic materials on potato brown rot control

Correction: The impact of biological soil disinfestation in conjunction with antagonists and organic materials on potato brown rot control

The impact of biological soil disinfestation in conjunction with antagonists and organic materials on potato brown rot control

The impact of biological soil disinfestation in conjunction with antagonists and organic materials on potato brown rot control

Anaeromicropila herbilytica gen. nov., sp. nov., a plant polysaccharide-decomposing anaerobic bacterium isolated from anoxic soil subjected to reductive soil disinfestation, and reclassification of Clostridium populeti as Anaeromicropila populeti comb. nov.

An obligately anaerobic bacterial strain (TB5T) was isolated from a soil sample subjected to reductive or biological soil disinfestation. Cells of the strain were Gram-stain-positive, spore-forming and motile rods. The strain grew at 15–40 °C (optimum, 37 °C) and pH 5.4–7.5 (optimum, pH 7.3). Strain TB5Tutilized a wide variety of carbohydrates including polysaccharides (cellulose, xylan, starch, inulin, glucomannan and laminarin) and organic acids. Acetate, ethanol, H2 and CO2 were products from the substrates utilized. The major components of the cellular fatty acids were C16 : 1 ω7c DMA, C16 : 0 DMA and C18 : 1 ω7c DMA. The diagnostic amino acid of the cell-wall peptidoglycan was meso-diaminopimelic acid. The closest related species to strain TB5T based on 16S rRNA gene sequences was Clostridium populeti 743AT (95.4 % sequence similarity). The genome size of strain TB5T was 5.09 Mb and the genomic DNA G+C content was 32.7 mol%. Strain TB5T had genes encoding polysaccharide-decomposing enzymes such as cellulase, xylanase, β-glucosidase and β-mannosidase in the genome. Based on the phylogenetic, genomic and phenotypic data, a novel species of a novel genus in the family Lachnospiraceae , Anaeromicropila herbilytica gen. nov., sp. nov., is proposed to accommodate the strain. The type species is Anaeromicropila herbilytica with strain TB5T (=NBRC 112093T=DSM 110037T) as the type strain. For the closest related species C. populeti , Anaeromicropila populeti comb. nov. is proposed with an emended description of the species.

Biological soil disinfestation compatible with renewable energy production for sustainable agriculture.

Biological soil disinfestation (BSD) is biotechnology to control soil-borne plant pathogens based on the anaerobic-reducing environment in soil and the functions of indigenous microbes. A new sustainable agricultural technology, the GET system, which produces and recovers methane as renewable energy from paddy fields, has a structure and principles similar to those of BSD technology. To confirm the potential of the GET system as BSD technology, the microbial community structures in the GET system were analyzed using next-generation sequencing. Thirty-four phyla were detected: 31 bacterial and 3 archaeal. Firmicutes dominated during the experimental period, which plays an important role in BSD functions such as organic decomposition, nitrate removal, and soil-borne pathogen elimination. The ability of the GET system to control soil-borne pathogens as well as produce renewable energy was demonstrated.

Anaerocolumna chitinilytica sp. nov., a chitin-decomposing anaerobic bacterium isolated from anoxic soil subjected to biological soil disinfestation.

An obligately anaerobic bacterial strain (CTTWT) belonging to the family Lachnospiraceae within the class Clostridia was isolated from an anoxic soil sample subjected to biological or reductive soil disinfestation. Cells of the strain were Gram-stain-positive, short rods with peritrichous flagella. The strain was saccharolytic and decomposed polysaccharides, chitin, xylan and β-1,3-glucan. Strain CTTWT decomposed cell biomass and cell-wall preparations of an ascomycete plant pathogen, Fusarium oxysporum f. sp. spinaciae. The strain produced acetate, ethanol, H2 and CO2 as fermentation products from the utilized substrates. The major cellular fatty acids of the strain were C16 : 1 ω7c dimethylacetal (DMA), C16 : 0 DMA and C18 : 1 ω7c DMA. The closely related species of strain CTTWT based on the 16S rRNA gene sequences were species in the genus Anaerocolumna with sequence similarities of 95.2-97.6 %. Results of genome analyses of strain CTTWT indicated that the genome size of the strain was 5.62 Mb and the genomic DNA G+C content was 38.3 mol%. Six 16S rRNA genes with five different sequences from each other were found in the genome. Strain CTTWT had genes encoding chitinase, xylanase, cellulase, β-glucosidase and nitrogenase as characteristic genes in the genome. Homologous genes encoding these proteins were found in the genomes of the related Anaerocolumna species, but the genomic and phenotypic properties of strain CTTWT were distinct from them. Based on the phylogenetic, genomic and phenotypic analyses, the name Anaerocolumna chitinilytica sp. nov., in the family Lachnospiraceae is proposed for strain CTTWT (=NBRC 112102T=DSM 110036T).

Implication of O2 dynamics for both N2O and CH4 emissions from soil during biological soil disinfestation

Soil O2 dynamics have significant influences on greenhouse gas emissions during soil management practice. In this study, we deployed O2-specific planar optodes to visualize spatiotemporal distribution of O2 in soils treated with biological soil disinfestation (BSD). This study aimed to reveal the role of anoxia development on emissions of N2O and CH4 from soil amended with crop residues during BSD period. The incorporation of crop residues includes wheat straw only, wheat straw with biochar and early straw incorporation. The anoxia in soil developed very fast within 3 days, while the O2 in headspace decreased much slower and it became anaerobic after 5 days, which was significantly affected by straw and biochar additions. The N2O emissions were positively correlated with soil hypoxic fraction. The CH4 emissions were not significant until the anoxia dominated in both soil and headspace. The co-application of biochar with straw delayed the anoxia development and extended the hypoxic area in soil, resulting in lower emissions of N2O and CH4. Those results highlight that the soil O2 dynamic was the key variable triggering the N2O and CH4 productions. Therefore, detailed information of soil O2 availability could be highly beneficial for optimizing the strategies of organic amendments incorporation in the BSD technique.

First report of Verticillium wilt caused by Verticillium dahliae on Russian olive (Elaeagnus angustifolia) in Iran.

Russian olive, also known as, Persian olive or oleaster (Elaeagnus angustifolia L.) is a species in the Elaeagnaceae family native to western and central Asia. In some orchards in Iran, intercropping Russian olive or Prunus trees with vegetables is a common practice. In 2018, about 130 ha of E. angustifolia orchards in Shahrood, Semnan Province, Iran showed branch wilting and dieback. Symptoms on affected trees started with yellowing of the lower leaves, followed by wilting and finally death of affected branches. Sections of stems indicated brown or black streaks in the vascular tissues under the bark. Isolations were made from discolored vascular tissues by surface-disinfesting small pieces of tissue with 0.5% sodium hypochlorite for 2 min, plating them onto potato dextrose agar amended with 25 mg/l streptomycin sulfate and incubated in the dark for 14 days at 25°C. Fungi consistently isolated from symptomatic tissues. Fungal isolates were identified as Verticillium dahliae Kleb. based on characteristics of verticillate conidiophores, hyaline, elliptical, single celled conidia measuring 4.7-6.0 × 2.3-3.4 μm (n = 100) and irregular, dark microsclerotia measuring 27-34 × 22-26 μm (n = 50) that developed after 14 days of growth at 25°C in the dark. The identification of two isolates was further confirmed by performing real-time PCR assay using a pair of specific primers for internal transcribed spacer (ITS) region of V. dahliae as previously described (Hiemstra et al. 2013). In addition, the molecular subdivision of isolates was further determined to discriminate D and ND molecular types (Keykhasaber 2017). According to molecular assays, isolates were identified as V. dahliae and grouped with ND types. The pathogenicity of isolates was evaluated by root-dipping one-year E. angustifolia seedlings (10 seedlings) into conidial suspensions of 1×107 cfu/ml. Inoculated plants were transplanted in pots containing autoclaved soil and maintained in a greenhouse at 25°C until symptoms appearance. Two seedlings were treated with sterile distilled water as controls. All inoculated seedlings started to show wilting symptoms similar to those present in naturally affected trees within 30 days after inoculation and died thereafter. Furthermore, V. dahliae was consistently isolated from symptomatic tissues. No symptoms were observed on the control plants. The pathogenicity test was repeated twice with similar results. To the best of our knowledge, this is the first report of Verticillium wilt on Russian olive trees in Iran. In Iran, Verticillium wilt is the cause of serious losses in many woody and herbaceous plants with economic importance including many trees belonging to the genus Prunus that are highly susceptible to the disease. In Shahrood (Semnan Province), most agricultural fields have a potato- or tomato- growing history. Verticillium wilt may become an important economic problem in many Russian olive and Prunus orchards in the future since their cultivation is expanding rapidly in many agricultural areas previously dedicated to tomato and potato crops, the majority of which are infested with V. dahliae. References Hiemstra, J. A., Korthals, G. W., Visser, J. H. M., Dalfsen, P. v., Sluis, B. J. v. d., and Smits, A. P. 2013. Control of Verticillium in tree nurseries through biological soil disinfestation. Pages 62-62 in: 11th International Verticillium Symposium, Georg-August-Universität,Göttingen, Germany, 5-8 May 2013, B. Koopmann and A. von Tiedemann, eds. DPG Spectrum Phytomedizin, Göttingen. Keykhasaber, M., Faino L., van den Berg, G.C.M., Hiemstra, J. A., Thomma, B. P. H. J. 2017. A robust method for discriminating defoliating and the non-defoliating pathotypes of V. dahliae. . In; Keykhasaber M. thesis 62-84. Sun, M., and Lin, Q. 2010. A revision of Elaeagnus L. (Elaeagnaceae) in mainland China. J. Systematics and Evolution 48:356-390.

\u03b2-1,3-Glucanase production as an anti-fungal enzyme by phylogenetically different strains of the genus Clostridium isolated from anoxic soil that underwent biological disinfestation

Biological (or reductive) soil disinfestation (BSD or RSD) is a bioremediation process to control soil-borne plant pathogens using activities of indigenous bacteria in the soil. Three obligate anaerobic bacterial strains (TW1, TW10, and TB10), which were isolated from anoxic soil subjected to BSD treatments, were examined for their abilities to produce anti-fungal enzymes. All strains were affiliated with the different lineages of the genus Clostridium. The three strains decomposed β-1,3-glucans (curdlan and laminarin), and β-1,3-glucanase activities were detected from their culture supernatants with these glucans. The three strains also produced the enzyme with wheat bran as a growth substrate and killed the Fusarium pathogen (Fusarium oxysporum f. sp. spinaciae) in the anaerobic co-incubation conditions. Observation by fluorescence microscopy of the pathogen cells showed that the three strains had degraded the fungal cells in different manners upon co-incubation with wheat bran. When the three strains were cultivated with the dead cells or the cell wall samples prepared from the Fusarium pathogen, strain TW1 utilized these materials as easily decomposable substrates by releasing β-1,3-glucanase. When observed by fluorescence microscopy, it appeared that strain TW1 degraded the mycelial cell wall nearly thoroughly, with the septa remaining as undecomposed luminous rings. In contrast, the other two strains decomposed neither the dead cells nor the cell wall samples directly. The results indicate that the various anaerobic bacteria proliferated in the soil under the BSD treatments should play key roles as an organized bacterial community to eliminate fungal pathogens, namely by release of anti-fungal enzymes with different properties.Key points•Three clostridial strains isolated from BSD-treated soils produced β-1,3-glucanase.•All strains killed the Fusarium pathogen in the anaerobic co-incubation conditions.•One of the strains produced β-1,3-glucanase with the fungal cell wall as a substrate.•The strain degraded the cell wall almost completely, except for the mycelial septa.

Production of \u03b2-1,3-glucanase and chitosanase from clostridial strains isolated from the soil subjected to biological disinfestation

Biological soil disinfestation (BSD) or anaerobic (reductive) soil disinfestation (ASD/RSD) is a bioremediation method used to eliminate soil-borne plant pathogens by exploiting the activities of anaerobic bacteria in soil. In this study, two obligate anaerobic bacterial strains isolated from BSD-treated soil and identified as Clostridium beijerinckii were examined for their abilities to suppress the spinach wilt disease pathogen (Fusarium oxysporum f. sp. spinaciae) as a representative soil-borne fungal plant pathogen. Both strains degraded β-1,3-glucan and chitosan, two major polysaccharide components of ascomycetes fungal cell wall, supplemented in the medium. β-1,3-Glucanase was detected in the supernatants of cultures supplemented with different types of glucan. Similarly, chitosanase was detected in cultures supplemented with chitosan. Both the enzyme activities were also detected in cultures containing glucose as a substrate. Live cells of F. oxysporum f. sp. spinaciae that were co-incubated with each anaerobic strain under anaerobic conditions using glucose as a substrate died during incubation. Freeze-dried dead fungal biomass of the pathogen, when added to the culture, supported good growth of both anaerobes and production of both enzymes. Severe and nearly complete degradation of both live and dead fungal cells during incubation with anaerobic bacteria was observed by fluorescence microscopy. When individual anaerobic bacterial strain was co-incubated with live pathogenic fungal cells in wheat bran, a popular material for BSD-treatment, both the strains grew well and killed the fungal pathogen promptly by producing both enzymes. These results indicate that both the bacterial strains attack the fungal cells by releasing extracellular fungal cell wall-degrading enzymes, thereby eliminating the pathogen.

Impacts on soil microbial characteristics and their restorability with different soil disinfestation approaches in intensively cropped greenhouse soils

The different impacts, especially on soil physicochemical and microbial characteristics, among disinfestation methods based on different principles (including physical, chemical, and biological) have not been illustrated well. Here, we used steam sterilization, dazomet fumigation, and reductive soil disinfestation (RSD) methods representative of physical, chemical, and biological soil disinfestation, respectively, to disinfest seriously degraded greenhouse soils before watermelon cultivation in one season. Compared with the control, RSD significantly decreased the soil nitrate content by 85.9% and the electrical conductivity by 52.0% and increased the soil pH to 7.44. Although all three soil disinfestations significantly decreased the abundance of the pathogen Fusarium oxysporum by 83.0-99.2%, their impacts on soil microbial characteristics were variable. Briefly, steam sterilization significantly changed multiple bacterial and fungal properties. Dazomet fumigation impacted mainly fungal properties, such as abundance, diversity, and community structure, but RSD significantly decreased bacterial diversity and altered the bacterial community structure. Although the differences mentioned above got smaller after watermelon cultivation, the plant performances differed dramatically in different soils. The largest plant biomass, fruit ratio, and yield were found in the RSD-treated soil, whereas the lowest fruit ratio and yield were found in the steam-sterilized soil. The soil nitrate content, electrical conductivity, bacterial diversity and community structure, and some specific microbial agents, such as Aspergillus, Cladosporium, and Pseudomonas, were correlated with plant performance. RSD is a promising soil disinfestation strategy to support plant growth in intensively cultivated greenhouse soils with serious problems, such as acidification, salinization, and pathogen accumulation.

Clostridium fungisolvens sp. nov., a new β-1,3-glucan-decomposing bacterium isolated from anoxic soil subjected to biological soil disinfestation.

Biological soil disinfestation (BSD) or reductive soil disinfestation (RSD) is a bioremediation method used to suppress or eliminate soil-borne plant pathogens by stimulating activities of indigenous anaerobic bacteria of the soil. An anaerobic bacterial strain (TW1T) was isolated from an anoxic soil sample subjected to the BSD treatment and comprehensively characterized. Cells of the strain were Gram-stain-positive, slightly curved and motile rods producing terminal spores. The strain was aerotolerant. Strain TW1T was saccharolytic and produced acetate, butyrate, H2 and CO2 as fermentation end products. Strain TW1T decomposed β-1,3-glucan (curdlan and laminarin) and degraded mycelial cells of an ascomycete Fusarium plant pathogen. Major cellular fatty acids of strain TW1T were C14 : 0, C14 : 0 dimethylacetal (DMA), C16 : 0 aldehyde and C16 : 0 DMA. Strain TW1T made a group on the phylogenetic tree constructed based on 16S rRNA gene sequences with species such as Clostridium fallax (96.3 %) and Clostridium polyendosporum (96.0 %). Whole genome analysis of strain TW1T showed that the total length of the genome was 5.28 Mb with the DNA G+C content of 31.3 mol%. The average nucleotide identity (ANIb) between strain TW1T and C. fallax was 71.2 %. Presence of the genes encoding laminarinase or GH16 β-glucosidase was confirmed from the genome analysis of strain TW1T. Based on the genomic, phylogenetic and phenotypic properties obtained, we propose strain TW1T should be assigned in the genus Clostridium in the family Clostridiaceae as Clostridium fungisolvens sp. nov. The type strain TW1T (=NBRC 112097T=DSM 110791T).

The families Ruminococcaceae, Lachnospiraceae, and Clostridiaceae are the dominant bacterial groups during reductive soil disinfestation with incorporated plant residues

Reductive soil disinfestation (RSD), alternatively called biological soil disinfestation or anaerobic soil disinfestation, is an environmentally friendly method used to control soil-borne diseases. Microorganisms are regarded as the key contributors for RSD; however, there is limited information on the relative importance of these microorganisms, which is essential for understanding the mechanisms underlying RSD. In this study, RSD was performed with four soils in a pot experiment, and the bacterial communities present during the RSD process were detected using MiSeq sequencing based on bacterial 16S rDNA. The results showed that RSD significantly changed the structure of the soil bacterial communities and reduced bacterial richness and diversity. The relative abundance of Firmicutes increased significantly, and the relative abundances of Actinobacteria and Acidobacteria decreased. Ruminococcaceae, Lachnospiraceae, and Clostridiaceae, which belong to Clostridiales within Firmicutes, were the three dominant bacterial families during RSD in most soils. Ruminococcaceae and Lachnospiraceae, rather than Clostridiaceae (previously identified as the key contributor), were strongly related to the pH decrease during RSD, which is considered an indicator for the accumulation of short-chain fatty acids. In addition to these bacterial groups, the families Sphingobacteriales, Bacillales, Burkholderiales, and Bacteroidales were enriched in some RSD-treated soils. In conclusion, the RSD treatment, soil type, and their interactions jointly influenced the bacterial communities and compositions in the RSD-treated soils.

Role of anaerobic bacteria in biological soil disinfestation for elimination of soil-borne plant pathogens in agriculture.

Biological soil disinfestation (BSD) or reductive soil disinfestation (RSD) is an environmental biotechnology to eliminate soil-borne plant pathogens based on functions of indigenous microbes. BSD treatments using different types of organic materials have been reported to effectively control a wide range of plant pathogens. Various studies have shown that development of reducing or anoxic conditions in soil is the most important aspect for effective BSD treatments. Substances such as organic acids, FeS, or phenolic compounds generated in the treated soil have been suggested to contribute to inactivation of pathogens. Additionally, anaerobic bacteria grown in the BSD-treated soil may produce and release enzymes with anti-pathogenic activities in soil. Clone library analyses as well as a next-generation sequence analysis based on 16S rRNA genes have revealed prosperity of obligate anaerobic bacteria from the class Clostridia in differently treated BSD soils. Two anaerobic bacterial strains isolated from BSD-treated soil samples and identified as Clostridium beijerinckii were found to decompose major cell wall polysaccharides of ascomycetous fungi, chitosan and β-1,3-glucan. C. beijerinckii is a species most frequently detected in the clone library analyses for various BSD-treated soils as a closely related species. The two anaerobic isolates severely degraded mycelial cells of the Fusarium pathogen of spinach wilt disease during anaerobic co-incubation of each isolate and the Fusarium pathogen. These reports suggest that antifungal enzymes produced by predominant anaerobic bacteria grown in the BSD-treated soil play important roles to control soil-borne fungal pathogens. Further studies using different bacterial isolates from BSD-treated soils are expected to know their anti-pathogenic abilities.

Degradation of the fungal cell wall by clostridial strains isolated from soil subjected to biological soil disinfestation and biocontrol of Fusarium wilt disease of spinach.

Biological soil disinfestation (BSD) involves elimination of soil-borne plant pathogens in an environmentally friendly manner. Two anaerobic bacterial strains (H110 and TB8) isolated from BSD-treated soil samples were analyzed for their roles in elimination of pathogenic fungi. The two strains were identified as Clostridium beijerinckii based on 16S rRNA gene sequences and phenotypic properties. The strains fermented various carbohydrates and produced acetate, butyrate, and n-butanol as major products as well as abundant gases (H2 and CO2). For evaluation of the antifungal potential of these strains, cells of a pathogen (spinach wilt disease, Fusarium oxysporum f. sp. spinaciae) were co-inoculated into anaerobic media with each anaerobic strain. After incubation for ~3weeks at 30°C, 10-30% of the cells of the pathogen survived when incubated without the anaerobic isolates, whereas the pathogen was eliminated when co-incubated with each anaerobe because of the growth of the anaerobic bacterium. It was found by microscopic examination that mycelial cells of the fungal pathogen were severely degraded during the first 3-7days of the co-incubation. The two strains utilized major cell wall polysaccharides of ascomycetous fungi-chitosan and ß-1,3-glucan (curdlan and laminarin)-as fermentative substrates added to the medium. Furthermore, both isolates degraded a cell wall preparation isolated from the mycelium of the Fusarium pathogen of spinach wilt disease. We concluded that the two anaerobic strains kill the pathogen of spinach wilt disease by degrading major fungal cell wall components as antifungal activities.

酸化還元研究の新展開-土壌の酸化還元がもたらす現象を追う- : 6. 低濃度エタノール処理による土壌酸化還元制御を利用した連作障害回避技術

酸化還元研究の新展開-土壌の酸化還元がもたらす現象を追う- : 6. 低濃度エタノール処理による土壌酸化還元制御を利用した連作障害回避技術

Effect of lignin-rich crop residues on the viability of Verticillium in organic greenhouse soils

Healthy soils are of vital importance for organic greenhouse cultivation. Due to the intensity of the cropping system, soil-borne diseases are of great concern. To achieve a more resilient system, growers use multiple strategies, including resistant rootstocks, organic soil amendments, biological soil disinfestation and plant stimulants. Soil-borne pathogens that form (micro) sclerotia are particularly difficult to manage due to their persistence in soil. Previous studies have shown that incorporation of lignin-rich crop residues can decrease the viability of microsclerotia of Verticillium longisporum in cauliflower fields. The purpose of this study was to evaluate the effect of lignin-rich amendments on the microsclerotia of V. dahliae in soils from organic greenhouses with a history of Verticillium wilt in solanaceous crops. In the laboratory, two greenhouse soils (river and sea clay) were mixed with 10% (w/w) broccoli (stem), bristle oat (whole plant), reed (stalks or leaves), Ethiopian mustard (whole plant) and corn (stalks or leaves). In the river clay soil, corn stalks, broccoli stem, reed and bristle oat significantly decreased the amount of viable microsclerotia. In the sea clay soil, only reed leaves and stalks had a significant effect. Only in the sea clay soil, a significant negative correlation was found between the amount of lignin added and the amount of viable microsclerotia detected. These results indicate that in the river clay soil, mechanisms other than lignin may be involved in Verticillium control. Surprisingly, real-time PCR analysis showed that the amount of Verticillium tricorpus was much higher than that of V. dahliae in both soils. Sequencing of a Verticillium strain isolated from the sea clay soil showed that it should be re-classified as Verticillium isaacii (formerly V. tricorpus). It is necessary to investigate the role of these different Verticillium species, before new control measures against Verticillium are further developed.

土壌還元消毒効果を示すClostridium sp.の検出と還元土壌から発生する気体のトマト萎凋病菌および青枯病菌の抑制効果

土壌還元消毒効果を示すClostridium sp.の検出と還元土壌から発生する気体のトマト萎凋病菌および青枯病菌の抑制効果

Biological Soil Disinfestation and Biofumigation: Alternatives for Chemical Fumigation in Organic Farming

Biological Soil Disinfestation and Biofumigation: Alternatives for Chemical Fumigation in Organic Farming

Nitrous oxide emissions during biological soil disinfestation with different organic matter and plastic mulch films in laboratory-scale tests

Nitrous oxide (N2O), which is a greenhouse gas, may be more emitted as an intermediate product of denitrification during biological soil disinfestation. The biological soil disinfestation is a method to suppress soil-borne pathogens under reductive soil conditions produced by the application of organic matter and water irrigation with plastic film. The objective of the study was to determine the effects of different organic matter and mulch films on N2O emissions during biological soil disinfestation. Grey lowland soil amended with cattle compost plus rice bran (0.2%), rice husk (0.2%) or dent corn (0.1%, 0.2% and 0.4%) was incubated at 100% water-holding capacity with or without plastic films made of polyvinyl chloride (PVC) and triple-layer polyolefin (3PO) for 72 h at 50°C. Permeation of the two films was also measured at 25°C and 50°C. Results showed that incorporation of organic matter increased N2O emissions compared with no organic matter addition at 50°C. Incorporation of rice bran and dent corn with easily decomposable C and low C:N ratios increased N2O emissions for the first 12 h, but thereafter, available C supply from these amendments suppressed N2O emissions. Permeability of mulch films increased at a higher temperature and was larger for PVC than for 3PO. Our study indicated that rice husk should not be used for soil disinfestation and that application rates of organic matter must be determined based on their decomposability. Moreover, mulch film covering would not suppress N2O emission in biological soil disinfestation because of high temperature.